EP0696141A2

EP0696141A2 - System for controlling different conditional access systems sending video, audio and data services and a receiver to be used in the system

Info

Publication number: EP0696141A2
Application number: EP95111375A
Authority: EP
Inventors: Mauri Kangas
Original assignee: Nokia Technology GmbH
Current assignee: Nokia Technology GmbH
Priority date: 1994-08-01
Filing date: 1995-07-20
Publication date: 1996-02-07
Anticipated expiration: 2015-07-20
Also published as: FI943582A0; FI97007B; DE69512335D1; EP0696141B1; DE69512335T2; FI97007C; FI943582A; EP0696141A3

Abstract

The present invention relates to a system for controlling different conditional access systems sending video, audio and data services to the receivers entitled to receive said services, wherein each conditional access system encrypts the service to be transmitted, sends encrypted the decryption keys required in the receiver and sends the authorization messages. At least one of the conditional access systems is nominated to control system entitled to control the encryption algorithms used by other conditional access systems and the sending of keys and authorization messages, whereby the control system can change rights of use of other conditional access systems in the receiver. The invention also relates to a receiver to be used in the system, consisting of a decoder (51) for receiving video, audio and data services and for decrypting the encryption, said decoder including tables (53) relating to the different conditional access systems, each of the tables including an algorithm list (55) used by the conditional access system, said list including the encryption algorithms in use for encryption of the messages and services of the conditional access system. Further, the decoder (51) comprises a control table (54) of the conditional access systems including a list of the control systems. In order to get the encryption information the receiver can be equipped with a releasable security module (52) the tables of which have the same kind of structure as the decoder (51).

Description

The present invention concerns a system for controlling different conditional access systems sending video, audio and data services to the receivers entitled to receive said services, wherein each conditional access system encrypts the service to be transmitted, sends encrypted the decryption keys required in the receiver and sends the authorization messages. The invention also concerns a receiver to be used in the system.
For transmission of digital video, audio and data signals it is possible to use either a transmission through air, satellite connection, cable television network, telephone/telenetwork or optical cable network, where digital information is transmitted to a large number of receivers. The digital information in question is often meant for free use of all receivers, but on the other hand, methods are required for controlling who/which of the receivers can get the information. This kind of transmission system has two lines of action in principle:

1) digital information is transmitted according to a predetermined plan, whereby each receiver can, either before or during the transmission, express his/her willingness to receive the information in question;
2) digital information is transmitted only in case some of the receivers expresses his/her willingness to receive this information.

In the latter case it is also possible to let others than the orderer to receive the information in question, so that these other receivers can have a previously agreed right to receive the transmission or they can order it during the transmission or while waiting it to be started. As in this kind of digital signal transmission the unauthorized receiving is wished to be prevented, the bit stream is changed in a form, where the receivers have no chance to decrypt the contents of the transmitted data, except if they have the use of the keys required for decrypting the data. There are numerous methods available for encryption of the digital bit stream, and the systems using them should be as complicated and secure as possible, in order to make sure that eventual unauthorized data decryption efforts after the introduction of the system will not be succesful.
An essential part of the transmission of digital video signals is the transmission of audiosignals and in addition, when implementing the systems there also has to be the so called control data transmitted. In order to diversify the services, it is necessary for different applications in the future also to send data information that from the point of view of the transmission system can include almost any kind of information. All these parts of information should be, at least where applicable, transmitted encrypted so as to make sure that only the selected receivers can receive the information.
The digital television systems of the future provide transmission of several programs simultaneously in one and the same transport channel. In that case the signal to be transmitted is in the packet form and packets including audio and video information of different programs travel in turn in the transport channel. Several compression standards have been developed for transmitting video, audio and data signals as packets, one of which is MPEG-2 (Moving Picture Experts Group). This standard has been created by a joint working team of ISO (International Standards Organisation) and IEC (International Electrotechnical Commission). Various MPEG standards have been developed and according to the specifications determined by them e.g. transmission of information is accomplished in several different applications in the future. As for the standard a reference is made to the MPEG standard ISO/IEC 13818 known in the art. Accordingly, the coded video, audio and data information is packetized in so called PES packets (Packetized Elementary Stream). A packet, the length of which can vary, includes a header and a data part.
Figure 1 illustrates the construction of a PES packet. The header of the packet consists of the packet start code prefix, the stream ID, indication of the packet length, optional header and a number of stuffing bytes. After that follows the information part of the packet including data bytes, which part, as mentioned earlier, can include a block of coded audio, video or data signals of the program, one packet, however, including only one kind of signals. The length of one packet can be several kilobytes.
The MPEG standard determines two different types of bit stream forms:
1) Program Stream and 2) Transport Stream. The program stream includes a coded video and audio signal as above mentioned PES packets (Packetized Elementary Stream), each of which includes respectively a coded block of bit stream of a particular size, in other words, the video, audio and data signal of the program source are separately coded and cut into blocks of particular lengths, each of which is placed in the information part of the PES packet. The length of the blocks and thus the length of the PES packet can vary. Thus the video signal of the program consists of successive video PES packets, the audiosignal of successive audio PES packets, etc. e.g. all the information of a movie can be recorded as a program stream.
Figures 2a and 2b illustrate how the PES packets of figure 1 are placed as program stream packets. The program stream, figure 2a, consists of successive packets including a header of the packet and an information part PACK. Figure 2b showing the structure of one program stream packet, the so called packet layer, illustrates, that the program stream packet PACK includes several PES packets marked with #1, #2, ...,#n, that can include picture, voice, data etc. relating to the program. For clarity it can be demonstrated that the packet sequence of figure 2a illustrates e.g. one movie, the PES packetized audio and video signals of which are placed in the information parts of the program stream packets. The program stream ends with the end code "program end code".
When sending the information of a program source to the transmission path there has to be formed a so called transport stream, that is meant for transmitting video and audiosignals on a transmission path like a television broadcast, satellite, cable TV, telephone/tele cables, optical cables etc. If the program source is a record in a form of the program stream, e.g. a movie recorded on a CD-record, the program stream is first demultiplexed to separate audio, video and data PES packets. In case the program source sends audio, video and data signals, they will be decrypted and formed to PES packets. Regardless of the type of the source, the thus formed PES packets are placed in the transport stream. The structure of the transport stream is illustrated in figures 3a and 3b. The transport stream consists of transport stream packets of a fixed size of e.g. 188 bytes, figure 3a. The packet includes a header of varied length and a data part called payload including payload information. Figure 3b illustrates the construction of one transport stream packet. The header of the packet comprises 9 fields, the last of which is the so called adaptation field. Bytes of the PES packet are placed in the payload of the packet.
Every system within the range of the digital signal transmission has in common the encryption of the digital signals, wherein the video, audio and data information included in the digital bit stream is first encrypted in an encryption device and then decrypted in a receiving device. Essential for the use of each system is the Conditial Access System sending control data encrypted to the receivers, the control data being used for sending receiving rights to the receivers and for sending keys relating to the bit streams. Several conditional access systems and, consequently, several different encryption algorithms to be used for transmission of their control data can be in use, and further, one and the same conditional access system can use several different algorithms for encrypting the control data. In general one program supplier uses only one conditional access system, but authorizing messages and key distribution messages of other conditional access systems (practically those of other program suppliers), can be attached thereto, and the encryption of the service is made by only one conditional access system and the used keys are told to other systems, so that they can send the keys encrypted with their own encryption algorithms. From the receiver's point of view it is usual that several different conditional access systems offer their services to one and the same receiver. Thus the receiver is able to receive services from several different program suppliers, because authorizing messages and key distribution messages controlled by several different conditional access systems have been received.
Thus the above mentioned conditional access system means practically a conditional access system of any pay-TV system providing programs and other services against payment to paying customers, so that on one hand rights of use can be safely given to all prospective customers and on the other hand it is possible to prevent receivers not having ordered and not willing to order said rights of use from receiving the services in question. Thus, the operation of the conditional access system, hereafter called the CA system, comprises as essential parts the following functions:

1. Encryption of the transmitted service subject to a charge.
2. Transmission of the keys required for decrypting the encrypted service.
3. Transmission of authorization messages to the receivers.

For decrypting the service transmitted against payment the decryption keys have to be sent safely to the orderer, so that the messages transmitting the required keys are encrypted with the algorithms used by the CA system. These algorithms are different from those used for encryption of the actual service, in other words the packets of video, audio and data transport stream. The authorization message means that the receivers are informed respectively through the so called authorization messages distributed to all receivers about the programs that the receiver can decrypt. This information is individual for each receiver, so that any kind of a sortiment of services to be received can be sent to each receiver. On the other hand, the receivers can be grouped so that a whole group of receivers gets the authorization with the same authorization message. Information included in the authorization messages has an individual code for each service which has to correspond to the code transmitted together with the keys, so as to make sure that the authorization is valid. The authorization messages can be sent individually because the decoder of each receiver has its own individual address number.
As due to the fast speed the encryption of the bit streams is a microcircuit implementation and can't be implemented with present-day technology through a program, it is in many cases profitable to implement the encryption on the bit stream level by using for different conditional access systems one and the same encryption algorithm, so that the encryption devices and decryption devices for different conditional access systems are at the hardware level in this respect the same.
When receiving programs of several different conditional access systems there are numerous problems. Whether or not the encryption on the bit stream level is the same for all digital signals, very soon in the future it will be the fact, anyway, that the transmission of digital signals is controlled by a great number of independent conditional access systems, each using several different algorithms of the control data, because of updatings and versions. It is true that each conditional access system has in general one characteristic way of transmitting the control data, but there can be several different versions of it. It is also possible, not very often practiced, however, that one conditional access system has several algorithms in use for transmitting the control data.
For security reasons it is used in known systems smart cards including the encryption keys for decrypting the data, the meaning of which is to act as so called controlled means to receive services transmitted encrypted and against payment. In general there are several offerers of services, so that there have to be several smart cards used either simultaneously or by changing the smart card. One smart card is generally activated to receive a service at a time and others can act only as receivers of information or be ready and waiting to be activated, when the respective service is selected from the receiver. Smart cards are reliable because their construction is very difficult or even impossible to be copied or misused. The term "smart card" means at the moment a card that includes one microprocessor circuit to be connected with the device itself through a serial line. The device supplies the electricity and the clock signal (oscillator) to the smart card in addition to the RESET signal. In the future there will surely be produced also smart cards with several circuits where the connection with the device itself is more complicated including e.g. a parallel-type connection.
In the above described situation the problem will be, how to solve the need to control uniquely the control data algorithms used by a certain conditional access system as well as the possibilities of different conditional access systems to give receiving rights or correspondingly keys for encrypted bit streams. This kind on need arises when wanting to prevent unauthorized receiving of encrypted digital signals, that could be based e.g. on an illegal distribution of receiving rights or keys or on the use of a poorly planned encryption algorithm of the control data, that for some reason can be used more widely than what had been planned also for passing the future algorithms or for decrypting the encryption at least partly. On the other hand, the market situation can sometimes lead to a situation, where a program supplier sells his own digital services by compensating the prices or rents of the receiving devices, and thus wants to make sure that any other program supplier can't use the receivers in question to distribute his own services - at least not without payment. In this kind of situation it will be necessary to control the use of the receiver, from the point of view of the program supplier who compensated the price or rent of the receiver. It is also possible that from some other quarter the program and algorithm data in headers of the transport stream packets of the conditional access system used by the program supplier is copied and programs will be sent illegally. This should preferably be prevented.
Using smart cards to minimize the security risks is also problematic. With respect to connections they are standardized and thus easily distributed to the receivers e.g. by mail. In this way the card can fall into the wrong hands and the information thereof can be copied and used to unauthorized receiving of services.
An object of this invention is to establish a system where the above mentioned problems caused by the use of many different conditional access systems can be solved. It is an object to create above the conditional access systems a system that determines for which purpose the receiver can be used and for which not.
Characteristic for the system is that at least one conditional access system has been nominated to control system entitled to control the encryption algorithms used by other conditional access systems and the sending of keys and authorization messages, whereby the control system can change rights of use of the other conditional access systems in the receiver. The receiver to be used in the system and including means for receiving encrypted video, audio and data services and for decrypting the encryption, is characterized in that said means include - tables relating to the different conditional access systems, each of the tables including an algorithm list used by the conditional access system, said list including the encryption algorithms in use for encrypting the messages and services of the conditional access system,

a control table of the conditional access systems including a list of the control systems.

The system above the conditional access systems according to the present invention is one or several conditional access system(s) getting more rights than the other conditional access systems, in other words it gets the right to control the rights and ways of use of the other conditional access systems. The system is hereafter called the control system.
As it can be appreciated from what has been stated above, the access management of the receivers can be divided into two parts: 1) management of the control data algorithms and 2) management of the conditional access systems. Thus, the present invention concerns a control system for managing the conditional access systems in respect of their characteristics. Both of the above mentioned fields of access management can be considered to be controlled at least on four principles: 1) by the number of the decoder, 2) by the code of the conditional access system, 3) by a combination of the above mentioned and 4) by a list of different control mechanisms. As the code of the conditional access system according to the proposal for a standard will comprise 256 alternatives for each conditional access system including eventual future variation of the conditional access system or the subsystems thereof, the control system of the receiver can be directed to all the 256 alternatives of a conditional access system, and subsystems of the conditional access system or each conditional access system can be equipped with a necessary mask word by which the subsystems of one conditional access system can be identified. Further, the receiver can have a list for different conditional access systems, including the above mentioned variations for each conditional access system or, correspondingly, a list of those conditional access systems that the receiver is not allowed to use.
The control system in accordance with the present invention can be made reliable so that the control of conditional access systems can not be effected uncontrollably, in other words, when manufacturing the device there will be determined the basic criteria by which the control system in future can be controlled. In the simpliest way, according to the first embodiment of the present invention, the control of the access system can be directed plainly to that code/those codes of the conditional access system, that is/are in use of the device supplier or his customer, and the rights of use in question can't be changed afterwards, unless the receiver were opened and the part in charge of the access rights replaced by a new one. In other words, when manufacturing the receiver it will be equipped with a list of the codes of the conditional access system or systems that have the right to control rights of use of the other conditional access systems.
According to an other embodiment for controlling the access right the system will be implemented flexibly, so that when manufacturing the device it can be equipped with the code of one conditional access system or several systems, that have the possibility not only to control the access right but also to change the codes that entitle to control the access rights. In other words, with help of the control systems included in the list to be feeded to the receiver when manufacturing, it is possible to add or remove codes of new conditional access systems, that is to change the list, whereas the list according to the first embodiment remains unchanged.
According to one characteristic of the invention it is used a separate part to be attached to the receiving device, the so called security module. In addition to the above mentioned lists it can include other electronic parts concerning the security like the parts required for decrypting the bit stream encryption. In addition to the decryption circuit, also the microprocessor of the receiver can be placed in it. An advantage of the security module is that if there appears to be a security risk, e.g. in connection with a wide illegal copying, the module can be changed to a new one in regard to its construction or contents. If necessary, the module can be constructed according to the receiving device so that it does not correspond to any standard. For the security this is a more effective alternative than only to change the smart card. Thereby the receiver can be used without or with the security module so that when receiving a certain service the decryption of messages is effected by the security module only, the receiver only or by the security module and the receiver together. Information of the required combination will be placed in the respective tables of the decoder and/or the module.
In the following the present invention will be described in more detail with reference to the enclosed drawings, where

Figure 1: illustrates the construction of a PES packet
Figures 2a and 2b: illustrate the construction of a program stream
Figures 3a and 3b: illustrate the construction of a transport stream
Figure 4: illustrates contents of successive packets of a transport stream
Figure 5: illustrates the construction of a receiver according to the invention
Figure 6: illustrates a list of algorithms
Figure 7: illustrates a list of conditional access systems

Figure 5 illustrates a decoder 51 according to the present invention with a separate security module (52) according to the present invention attached thereto. The both of them are placed in the receiver, whereby the functions included in the decoder and security module have been assembled already when manufacturing. The both include two kinds of tables: 1) numerous conditional access system tables 53 (CA_system info table) and 2) a control table of conditional access systems 54 (CA_system control list). The conditional access system table 53 includes an algorithm list 55 (algorithm list) and a version list of conditional access systems 56 (CA_version list). The algorithm list 55 includes a list of encryption algorithms eventually in use, by which the messages of the conditional access system have been encrypted. Correspondingly, the version list 56 includes a list of the versions of the respective conditional access system 53 that can be in use, whereas the control list of the conditional access systems 54 includes a list of those conditional access systems by which the rights of use of conditional access systems can be changed. As according to the basic idea of the invention one conditional access system or several systems get the right to control other conditional access systems, the list of these control systems having more rights is thus included in the control table 54.
Figure 6 A shows the contents of the algorithm list 55 of figure 5. In consists of two adjacent lists relating to the actual algorithm list ALGORITHM, the first list OWN SEL for the own use of the conditional access system and the other list CTRL_SYS SELECTION for the control system of the conditional access systems. The column marked with X means that the respective algorithm is in use. E.g. algorithm ALG#2 is in use of the control system of conditional access systems whereas algorithms ALG#1 and ALG#3 are as well in the own use of the conditional access system as in use of the control system of the conditional access systems. The algorithm selection part ALG_SELECTION on the bottom of the list is adjustable by the control system. That means that the algorithms are selected either by the control system or by the conditional access system but the decision between these two alternatives will be made by the control system of the conditional access systems. The control system can e.g. let the conditional access system CA_SYSTEM#1, figure 5, decide, that the algorithm ALG#3 will be used for encrypting the messages transmitted by it. In the situation of figure 6A the value of the selection part ALG_SELECTION is CTRL_SYS, in which case the algorithms are selected by the control system.
Correspondingly figure 6B shows the contents of the version list 56 of figure 5 in more details. The figure illustrates the version table of conditional access systems CA_VERSION LIST, that has a separate column OWN_SEL for the conditional access system and a separate column CTRL_SYS SELECTION for the control system of the conditional access systems. Like in figure 6A there is a choice made by the control system between the conditional access system and the control system on the bottom of the list. The version is selected either by the control system or the conditional access system but the decision which of them can choose, is made by the control system of the conditional access systems. The control system can e.g. let the conditional access system CA_SYSTEM#1, figure 5, decide, that the version VER#1 of the conditional access system will be used. In addition to different versions of the conditional access systems, the version system includes also programming differences between the different versions, so that this selection provides also the selection of different program versions in addition to the versions of the conditional access system. In the situation of figure 6B the value of the selection part VER_SELECTION is CTRL_SYS, so that the version is selected by the control system, which means that either version VER#1 or VER#3 can be selected for the use of the conditional access system.
Figure 7 shows the contents of the control table 54 of the conditional access systems of figure 5 (CA_SYSTEM CONTROL LIST). There is a list of possible conditional access systems SYS#1,...,SYS#n in two columns, first of which, CA_SYS IN USE, gives the conditional access systems in use, in figure the systems 1, 3, 5 are in use, and the other CA_SYS NOT IN USE gives the conditional access systems the use of which absolutely has to be prevented, in figure the systems 2, 4 and 6, etc. In addition, the table includes a third column CONTROL CA_SYSTEM IN USE, where those conditional access systems are listed that act as control systems. This list needs the security arrangements so that at least one control system remains valid when manufacturing and can't be removed from the list. The lists CA_SYSTEM IN USE and CA_SYSTEM NOT IN USE also include the information, which security modules/smart cards can be attached to the receiver in question and correspondingly in case of a security module there is also the information, which receiver system the security module can be attached to (this information is not shown in figure 7). In this way a situation where a particular receiver can only be equipped with desired security modules or smart cards can be controlled.
In the following reference is made again to figure 5, and the security module 52 used together with the smart card in the receiver is described in more details. The security module 52 includes matters from the same points of view as the tables of the decoder 53, but the tables included in the security module and the decoder do not have to have anything in common but the tables can include quite different things than the corresponding table of the decoder. If there appears to be a security risk, e.g. in connection with a wide piracy, the security module can be changed to a new one in regard to its construction or contents, whereby the illegal copying can be prevented or made more complicated and thus a safe system guaranteed. As the known smart cards are standardized in respect of the connection and can be easily distributed e.g. by mail, the security risk of the smart card is bigger compared with the security modules that are bigger in size. A separate security module can be constructed so that the connection with the device, unlike the same with the smart card, is not in accordance with any standard, whereby there is no use of examining a security module of one device manufacturer in respect of piracy or for examining a security module of some other manufacturer. Further, the security module can include such ASIC circuits the illegal copying of which is difficult, because the function of it can be very complicated.
The security module according to the invention is a releasable module that is connected with the device itself through a connector. When speaking about a security module containing more than just a smart card, it means a module with a multipole connection (depending on the application) with the receiver. This kind of security module can contain in principle the same kind of electronics known by the present technology e.g. in receiving devices. As the physical size of the security module or the electronics included therein is not limited like in case of the smart card (bending, thickness of the card etc.) electronic security parts can be placed in it, e.g. for the transmission of digital signals, parts for decrypting the bit stream encryption. As on the other hand it can be complicated to make a connection between the microprocessor and the decryption circuit of the bit stream encryption, safe enough from the point of view of the security, these parts can be placed in the security module as well, if necessary. In addition to these measures it is the purpose to construct the security module so that it would be as difficult as possible to examine the parts of it with electronic equipment.
As mentioned earlier, the security module includes tables with the same construction as the decoder. According to the idea of the security module, however, the information included in it differs from what has been set usually in the decoder by the manufacturing. Therewith it is possible to add new conditional access systems and encryption algorithms for the receiver and to make illegal copying more difficult. A separate security module and a smart card attached thereto can both include said tables, but as concept and to make matters more simple the above mentioned cases have all been combined in the concept of the security module. Thus the tables of the security module can be a combination of tables of a separate module and a separate smart card. The meaning of the tables is to manage situations, where the receiver is intended for receiving transmissions controlled by different conditional access systems.
The receiver can be used either without or with a security module, so that for receiving a certain service the messages are decrypted a) with the security module only, b) with the receiver only or c) with the security module and the receiver together. The information about the required combination is placed in some tables of the decoder and/or the security module.
The system as well as the receiver and the security module according to the present invention provide a transmission and receiving system of video, audio and data services, that is easier to be controlled and that at the same time makes the illegal receiving of encrypted services more difficult.

Claims

A system for controlling different conditional access systems sending video, audio and data services to the receivers entitled to receive said services, wherein each conditional access system encrypts the service to be transmitted, sends encrypted the decryption keys required in the receiver and sends the authorization messages that include at least information about those programs that the receiver is entitled to decrypt, characterized in that at least one of the conditional access systems is nominated to control system entitled to control the encryption algorithms used by other conditional access systems and the sending of keys and authorization messages, whereby the control system can change rights of use of other conditional access systems in the receiver.
A system in accordance with claim 1, characterized in that with said at least one control system also control systems can be controlled, whereby said control system can be used for nominating new control systems and removing those.
A receiver for receiving video, audio and data services, said receiver comprising a decoder (51) for receiving encrypted video, audio ad data services and decrypting the encryption, characterized in that said decoder (51) comprises
- tables (53) relative to different conditional access systems, each including an algorithm list (55) used by the conditional access system, said list consisting of encryption algorithms in use, by which the messages and services of the conditional access system have been encrypted,

- control table (54) of conditional access systems including a list of control systems.
A receiver in accordance with claim 3, characterized in that it comprises a detachable security module (52) also including
- tables (53) relative to different conditional access systems, each including an algorithm list (55) used by the conditional access system, said list consisting of encryption algorithms in use, by which the messages and services of the conditional access system have been encrypted,

- control table (54) of conditional access systems including a list of control systems.
A receiver in accordance with claim 3 or 4, characterized in that each table (53) relative to the conditional access system further includes a version list (56) of the conditional access system including a list of those versions of the respective conditional access system (53), that are in use.
A receiver in accordance with claim 3 or 4, characterized in that each algorithm of the algorithm list (55) has a first information (OWN SEL) telling if the algorithm is in the own use of the conditional access system, and an other information (CTRL_SYS SELECTION) telling, if the algorithm is in use of the control system.
A receiver in accordance with claim 6, characterized in that the control system decides, if the algorithm is selected by the control system or the conditional access system.
A receiver in accordance with claim 5, characterized in that each version of the conditional access system (53) mentioned in the version list (56) of the conditional access system has a first information (OWN SEL) telling, if the version can be selected for use of the conditional access system by the conditional access system, and an other information (CNTRL_SYS SELECTION) telling if the version can be selected for use of the conditional access system by the control system.
A receiver in accordance with claim 3 or 4, characterized in that the control system decides, if the version will be selected by the control system or the conditional access system.
A receiver in accordance with claim 3 or 4, characterized in that the control table (54) of conditional access systems includes a first list (CA_SYSTEM NOT IN USE) indicating those conditional access systems that are not in use of the receiver, and an other list (CA_SYSTEM IN USE) indicating those conditional access systems that are in use of the receiver.
A receiver in accordance with claim 3, 4 or 10, characterized in that the control table (54) of the conditional access systems includes a list (CONTROL CA_SYSTEM IN USE) indicating the conditional access systems acting as control systems.
A receiver in accordance with claim 11, characterized in that said list of control systems comprises a security system to secure that at least one control system is such that it cannot be removed from the list.
A receiver in accordance with claim 3 or 4, characterized in that the information included in the tables of the conditional access systems (53) and the information included in the control table (54) of the conditional access system are recorded in the receiver when the receiver is manufactured.
A receiver in accordance with claim 13, characterized in that the information included in the tables of the conditional access systems (53) and the information included in the control table (54) of the conditional access system can be updated with the encrypted messages received together with the received data.
A receiver in accordance with claim 13, characterized in that the information of the tables of the conditional access systems (53) and the information of the control table (54) of the conditional access system can be updated with a smart card to be connected with the receiver.
A receiver in accordance with claim 15, characterized in that it has a connection for connecting the smart card with the security module (52).
A receiver in accordance with claim 4, 15 or 16, characterized in that the receiver (51) includes an information of, which kind of security modules and smart cards can be connected with it.
A receiver in accordance with any of the claims 3 to 17, characterized in that when receiving a certain type of service, only information saved in the receiver (51) is used for decrypting messages.
A receiver in accordance with any of the claims 3 to 17, characterized in that when receiving a certain type of service, only information saved in the security module (52) is used for decrypting messages.
A receiver in accordance with any of the claims 3 to 17, characterized in that when receiving a certain type of service, information saved both in the security module (52) and in the receiver (51) is used for decrypting messages.
A releasable security module (52) for a receiver receiving video, audio and data services, consisting of a decoder (51) for receiving encrypted video, audio and data services and for decrypting the encryption, said security module including information for the decoder for decrypting the encrypted service, characterized in that it comprises
- tables (53) relative to different conditional access systems, each table including an algorithm list (55) used by the conditional access system, said algorithm list including a list of encryption algorithms in use, by which the messages and services have been encrypted,

- a control table (54) of conditional access systems including a list of control systems.
A security module in accordance with claim 21, characterized in that it has the information of, which kind of receiver it can be connected with.